The resistance of sensors based on Magnetoresistance (MR), such as Giant Magnetoresistance (GMR) or Tunnel Magnetoresistance (TMR) sensors, varies when an external magnetic field is applied to the sensor device. Magnetoresistance angle sensors are widely used in non-contact angular position sensors in harsh environments like in automobiles or industry. In general, these sensors are relatively insensitive to wear and contamination.
Magnetoresistance “spin valve” sensors typically have two magnetic layers separated by a non-magnetic layer. One of the two magnetic layers is pinned so that it has a fixed orientation in a reference direction, while the other layer is a free layer that changes orientation in response to an external magnetic field.
GMR angle sensors, for example, use bridge configurations with one resistor that reduces its resistance and another than increases its resistance when a certain physical magnitude is applied. For GMR spin-valve sensors, this can be accomplished by using GMR sensor resistors for the legs of the bridge that are magnetized in two different reference magnetization directions. To fix the reference magnetization direction, the structure is heated, an external magnetic field is applied then the structure is cooled to fix the magnetization direction.
For monolithically integrated sensors requiring multiple magnetization directions, this process must be repeated for each magnetization direction. To prevent over-writing the previously fixed magnetizations, typically a localized magnetization process is applied, such as by a local heating (for example, by monolithically integrated heating stripes or a laser spot) within an external magnetic field then cooling to fix the magnetization direction. This process has to be conducted for each magnetization direction, which adds complexity and cost to the manufacturing process.